FIG. 1 illustrates a conventional bead bed 1 having a patient 2 lying thereon. The bed 1 generally comprises in combination a box-like tub 3 of sufficient size to accommodate the patient thereon and ceramic beads 4 filling the tub 3. The beads 4 are coated with resin, for example, and are made of finely divided glass having a specific gravity of approximately 2 to 3 and a particle size of 50 to 150.
An air permeable filter sheet 5 is fixedly attached to the peripheral edges of the tub 3 to cover the upper surface thereon. The mesh of the filter sheet 5 is smaller than the particle size of the beads 4. A plenum chamber 6 is located at the lower part of the tub 3 and a porous air diffusion plate 7 separates the plenum chamber 6 from the tub 3. An air blower 9 is provided within a machine housing 8 and the housing 8 also serves as a base for the bed. A conduit 10 is coupled between the air blower 9 and the plenum chamber 6 to supply compressed air thereto. A radiator 11 is provided in the conduit 10. Sheet press members 12 retain the sheet 5 at the peripheral edges of the tub 3.
In such arrangement, the compressed air is supplied from below through the plenum chamber 6 and the air diffusion plate 7 to the interior of the tub 3 by operation of the air blower 9. Once the interior of the tub 3 is fully supplied with the compressed air, the beads 4 contained in the tub 3 by means of the filter sheet 5, float under the influence of the compressed air. The specific gravity of the beads 4 is lowered to approximately 1.1 to 1.2 in such a condition and, thus, the patient 2 lying on the bed is supported in a floating state.
In a bead bed, contact pressure applied to the patient 2 is lessened significantly and the patient feels like he is floating in the air. After passing through the interior of the bed tub, the air passes through the sheet 5 into the interior of a room. It will be noted that the temperature of the air supplied from the air blower 9 is increased by 10.degree. to 20.degree. during the compression stroke. For this reason, a radiator 11 is provided in the conduit 10.
A bead bed arrangement has the advantage that when used for medical purposes, the effectiveness of treatment is improved by supplying the air in a constant manner while restraining application of contact pressure to the affected part of the patient suffering from a burn, for example. Bedsores are prevented by lessening the contact pressure between the bed and the patient.
The filter sheet adapted to cover the upper surface of the bed tub 3 is generally stained with the patent's body fluids. The filter sheet is usually made from a fabric woven of synthetic fiber such as polyester resin and the like, which is excellent in washability and durability. When the beads float under the influence of the air during operation of the bed, static electricity is likely to occur due to friction between the beads and between the beads and the filter sheets. Further, it has been found that the static electricity thus generated may reach 12 to 20 KV by actual measurement. As a result, an electric shock may be imparted to a nurse or attendant in charge of the patient and to the patient himself when he leaves and returns to his bed. An electric shock of this magnitude is not only painful but may also cause critical damage to the patient, particularly to a patient suffering from heart diseases.